1. Field of the Invention
The present invention relates to a headlamp for a car or other vehicles. More specifically, the present invention relates to a headlamp using a metal halide discharge lamp such as an iodine lamp for a light source, in which is difficult to include two light sources for the high beam and the low beam.
2. Background Art
An example of a headlamp in the prior art that uses a discharge lamp as a light source and has a switch mechanism for selecting the high beam distribution or the low beam distribution is disclosed in Japanese Unexamined Patent Publication No. Hei 8-111101. As shown in FIG. 10, the principal part of the headlamp 90 includes a discharge lamp 91, a reflecting mirror 93 and a lever 92 that is placed vertically with a rocking pin 92a disposed above the discharge lamp 91. The discharge lamp 91 is attached to the lever 92, and the light source 91a that is a burner of the discharge lamp 91 is positioned substantially on the optical axis Z when the discharge lamp 91 is in the low beam position. When switching to the high beam position, the lever 92 is rotated in the backward direction for a predetermined angle .alpha. around the rocking pin 92a by the actuator 94 such as a motor or a solenoid. Then, the position of the discharge lamp 91 is moved backward and downward from the low beam position with respect to the reflecting mirror 93, so that the discharge lamp 91 moves into the high beam position.
However, in the above-mentioned switching mechanism for selecting the high beam distribution or the low beam distribution in the prior art, it is essential to maintain very high accuracy of the relative position of the light source 91a to the reflecting mirror 93 in order to obtain a predetermined characteristic of the light distribution. Therefore, the light source 91a should be moved between the low beam position and the high beam position with high accuracy. However, the accuracy can be deteriorated by vibration, an impact, an abrasion due to a repeated movement of the light source or other factors when the car is moving. In order to solve this problem, the known mechanism is complicated and large, resulting in a high cost.